SEATTLE (CBS Seattle/AP) — The Seattle Transportation Department admits it made a mistake with deicer that caused some accidents Dec. 2 and shut down the West Seattle Bridge.

Road maintenance manager Steve Pratt told a city council committee Tuesday they were trying to get ahead of anticipated freezing weather and Monday night football traffic when they sprayed magnesium chloride on the roadway that afternoon.

KIRO-TV reports it was too warm at the time — more than 40 degrees — and the operator mistakenly applied twice the recommend amount — 30 gallons per lane mile, instead of 15.

“We were trying to be pro-active,” Pratt told the council.

The result? Instead of preventing a slick roadway, the deicer created slippery pavement.